(1) Field of the Invention
The present invention relates to a multi-layer drawn polyester vessel. More particularly, the present invention relates to a gas-barrier vessel comprising a gas-barrier layer composed of an ethylene/vinyl alcohol copolymer and a substrate layer composed of a polyester, in which the vessel wall is molecularly oriented in at least one axial direction by drawing and the interlaminar adhesion is improved.
(2) Description of the Prior Art
Formation of vessels such as drawn polyester bottles is popular at the present. These formed vessels have excellent transparency and appropriate gas-barrier property, and they have been broadly used as vessels for liquid detergents, shampoos, cosmetics, soys and sauces and recently also for carbonated drinks such as beer, cola and soda pop and refreshing drinks such as fruit juices and mineral water.
However, since even drawn polyester bottles are plastic vessels, they have a permeability to oxygen, carbon dioxide gas and the like though the permeability is very small, while the gas permeability of completely sealed vessels such as glass bottles and metal cans is substantially zero. Accordingly, drawn polyester bottles are inferior to cans and glass bottles in the food filling and storing properties, and in case of carbonated drinks, loss of carbon dioxide gas is caused and in case of beer, cola and soda pop, there is a difinite limit of the storage period.
As means for improving the gas barrier property in drawn polyester vessels, there has been practically adopted a method in which a drawn polyester bottle is coated with a polyvinylidene chloride resin. Lamination or coating of a polyester with a resin having a poorer gas-barrier property than that of the polyester is insignificant for improving a drawn polyester resin which has inherently an appropriate gas-barrier property. Namely, a resin which is excellent over a polyester in the gas-barrier property should be used for lamination or coating. As such resin, there can be mentioned thermoplastic resins selected from vinyldiene chloride resins, acrylonitrile type resins and vinyl alcohol type resins. At any rate, an appropriate resin should be selected while the properties and processability of the resin are taken into consideration.
We previously found that in the production of a multi-layer drawn polyester vessel comprising a polyester substrate and a gas-barrier layer of an ethylene/vinyl alcohol copolymer, if the steps of forming a pipe by co-extrusion, cutting the pipe, heat-forming the bottom and biaxially draw-blowing the bottomed tube are combined in this order, a multi-layer drawn polyester vessel having an excellent gas-barrier property and a high molecular orientation can be obtained (see Japanese Patent Application No. 73893/83).
However, since there is no substantial heat bondability between the polyester layer and the ethylene/vinyl alcohol copolymer layer, it is eagerly desired to develop an adhesive resin which can provide such a strong interlaminar bonding between both the layers that the bonded structure can resist falling shocks.